A fixing device for a cap screw as a fastening screw has become known from DE-GM 18 20 586. A flange can be fastened to a structural component by means of this fastening screw. At least one hole with a preassembly thread is provided in the flange. The fastening screw has a shank area between the head and the threaded area, whereby the length of the threaded area for fastening the fastening screw is dimensioned such that this screw leaves the preassembly thread to be traversed within the framework of the preassembly before the screwing-in process in the fastening thread begins. In this case, the thread inner diameter of the fastening screw corresponds to the outer diameter of the shank area, as a result of which the loss protection of the fastening screw is realized. This means that the fastening screw is only held in the hole by the small threaded area in case of the solution according to DE-GM 18 20 586.
Also, a necked-down screw, which is used to seal a threaded hole, is disclosed in DE 15 30 27 417 A1. The shank area of this fastening screw is provided with a coating made of elastomer material, whose outer diameter corresponds to the outer diameter of the thread. An exclusively elastic, that is, reversible deformation of the elastomer material should take place during the screwing in.
The fastening systems of the type mentioned in the introduction are also used, for example, to fasten preassembled structural components, such as steering column modular units, or the like, to the body of a motor vehicle within the framework of the final assembly. In this case, in the preassembly of a steering column modular unit, one or more fastening screws are each screwed into a preassembly thread which is preferably fastened to the housing of the steering column modular unit. This has the advantage that, in the final assembly of the steering column modular unit to the body, no individual fastening structural elements have to be additionally provided. If the steering column modular unit is brought into its final position during the final assembly to the body, then the fastening screws are screwed into a second fastening thread. This fastening screw may be located both directly on the body structure of a motor vehicle and/or likewise as an extension of the preassembly thread on the steering column housing. In the latter case, the steering column modular unit is clamped by means of a bracket on the body side, which is arranged between the preassembly thread and the fastening thread. Both forms of fastening make it necessary that the fastening screw with its thread must have left either the preassembly thread before the screw enters the fastening thread with its first turns, or the preassembly thread is broken over, i.e., destroyed, during the entry of the fastening screw into the fastening thread.
Both assembly variants described have a serious drawback in terms of a possible disassembly of the steering column modular unit again.
The variant mentioned first, in which the fastening screw came completely out of the preassembly thread, results in the difficulty that a loosening of the fastening screw means inevitably a return of the screw into the first preassembly thread. In the usually only possible introduction of a pressing power in the longitudinal axis of the screw, this return is very difficult and is almost entirely ruled out under normal disassembly conditions. This means that the disassembly of the steering column is possible only with special difficulties.
In the second of the variants described above the preassembly thread is already often almost entirely destroyed after the initial assembly of the steering column. This means that, after a disassembly of the steering column, this thread must be rethreaded, since it is no longer usable, and as a result, the steering column is limited in its ability to be assembled.